1. Field of the Invention
The present invention relates to an internal combustion engine including a first fuel injection mechanism (in-cylinder injector) for injecting fuel towards a cylinder and a second fuel injection mechanism (intake manifold injector) for injecting fuel towards an intake manifold or an intake port. Particularly, the present invention relates to the technique of achieving combustion stabilization even in the case where abnormality occurs in the fuel supply system that supplies fuel to the first fuel injection mechanism.
2. Description of the Background Art
An internal combustion engine is well known, including an intake manifold injector for injecting fuel into the intake manifold of the engine and an in-cylinder injector for injecting fuel into the engine combustion chamber, wherein the fuel injection ratio of the intake manifold injector to the in-cylinder injector is determined based on the engine speed and engine load.
In the event of operation failure due to a malfunction of the in-cylinder injector or the fuel system that supplies fuel to the in-cylinder injector (hereinafter, referred to as high-pressure fuel supply system), fuel injection by the in-cylinder injector will be ceased.
On the basis of the fail-safe faculty in such operation failure, it is possible to ensure travel by inhibiting fuel injection from the in-cylinder injector and fix the combustion mode at the uniform combustion mode to effect fuel injection from the intake manifold injector alone. However, in the case where the intake manifold injector is set to take an auxiliary role of the in-cylinder injector, fuel of a quantity corresponding to the intake air at the time of full opening of the throttle valve cannot be supplied, whereby the air-fuel ratio in the fail-safe mode will become lean. There may be the case where the torque is insufficient due to combustion defect.
Japanese Patent Laying-Open No. 2000-145516 discloses an engine controlling device that can maintain the air-fuel ratio properly to obtain suitable driving power even during fuel injection control by the intake manifold injector alone in the fail-safe mode caused by operation failure of the in-cylinder injector. This engine controlling device includes an in-cylinder injector that directly injects fuel to the combustion chamber, an intake manifold injector that injects fuel to the intake system, and an electronic control type throttle valve. When the target fuel injection quantity set based on the engine operation state exceeds a predetermined injection quantity of the in-cylinder injector, the engine controlling device compensates for the insufficient quantity by fuel injection from the intake manifold injector. This engine controlling device also includes an abnormality determination unit determining abnormality of the in-cylinder injector and the high-pressure fuel supply system that supplies fuel to the in-cylinder injector, a target fuel correction unit comparing the maximum injection quantity of the intake manifold injector when abnormality is determined with the target fuel injection quantity to fix the target fuel injection quantity at the maximum injection quantity when the target fuel injection quantity exceeds the maximum injection quantity, a target intake air quantity correction unit calculating the target intake air quantity based on the target fuel injection quantity fixed at the maximum injection quantity and the target air-fuel ratio, and a throttle opening indication value calculation unit calculating the throttle opening indication value with respect to an electronic control type throttle valve based on the target intake air quantity.
When abnormality is sensed in the in-cylinder injector and the high-pressure fuel supply system that supplies fuel to the in-cylinder injector in this engine controlling device, the maximum injection quantity of the intake manifold injector is compared with the target fuel injection quantity that is set based on the engine operation state. When the target fuel injection quantity exceeds the maximum injection quantity, the target fuel injection quantity is fixed at the maximum injection quantity. The target intake air quantity is calculated based on this fixed target fuel injection quantity and target air-fuel ratio. The throttle opening indication value is calculated with respect to the electronic control type throttle valve based on the calculated target intake air quantity. Accordingly, when abnormality is sensed in the in-cylinder injector system, fuel injection from the in-cylinder injector is inhibited, and fuel is to be injected from only the intake manifold injector. Based on the maximum injection quantity at this stage and the target air-fuel ratio, the target intake air quantity is calculated. The throttle opening indication value with respect to the electronic control type throttle valve is calculated based on the target intake air quantity. In the fail-safe mode corresponding to failure in the in-cylinder injector system, the throttle opening will open only to the level corresponding to the target air-fuel ratio no matter how hard the acceleration pedal is pushed down. Thus, the air-fuel ratio is maintained properly to obtain suitable driving power.
It is to be noted that the engine controlling device disclosed in Japanese Patent Laying-Open No. 2000-145516 inhibits fuel injection from the in-cylinder injector to conduct fuel injection from only the intake manifold injector when malfunction occurs in the high-pressure fuel supply system. Essentially, fuel is injected from only the in-cylinder injector at the region of high rotation and high load. Since the fuel injected into the cylinder is at high pressure in this context, the fuel is readily atomized due to the large shearing force generated with respect to the intake air. Therefore, a high combustion rate is realized even if the flow of the intake air is absent of a vortex (whirl flow such as a tumble flow that is a vertical whirl, or a swirl flow that is a lateral whirl).
If fuel is injected from only the intake manifold injector with fuel injection from the in-cylinder injector inhibited, as in Japanese Patent Laying-Open No. 2000-145516, the whirl flow in the combustion chamber will not be generated actively. The combustion rate is reduced to render combustion unstable. There is also the possibility of the exhaust temperature being too high.